The present assignee has developed certain systems for speech interpretation on which several patents have issued.
An automatic speech interpreter, as disclosed in U.S. Pat. No. 3,812,291 issued May 21, 1974 and assigned to the assignee of the present invention, is essentially an acoustic pattern recognition device. Acoustically isolated utterances, such as words or phrases, are normalized by an information-theoretic compression technique that removes the effect of talker cadence and, to some degree, the effect of speaker variability. The resulting 120-bit pattern is then correlated with reference patterns derived through a training process. The only requirement for accurate recognition is reasonable acoustic separation between the patterns. The system can be retrained on-line for new vocabularies, speakers or acoustic environments at the rate of about 5 seconds per vocabulary utterance. A voice command system using this technique has been demonstrated with a large number of vocabularies of up to 100 words and in several languages. A unique feature is the ability to operate the system over commercial telephone circuits.
The present invention represents a significant improvement to the encoding and classification technology covered, in part, under U.S. Pat. No. 3,812,291 and U.S. Pat. No. 3,582,559 also assigned to the present assignee. Although this invention incorporates a number of logical processes common to those patents, it also incorporates critical differences that yield substantially improved signal classification accuracy while dramatically reducing the requirements for buffer storage of unencoded signal data. These improvements have been measured by operating the present invention as a word recognition device and comparing classification performance with that obtainable using a similar device incorporating the invention described in U.S. Pat. No. 3,812,291. Test material consisted of 1000 prerecorded utterances taken from a 100-word vocabulary designed to span the sounds of the American English language in a balanced fashion. Using these test data, the present invention yielded an average 40% reduction in classification errors when compared with the performance of the invention described in U.S. Pat. No. 3,812,291.